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United States Patent |
5,113,581
|
Hidese
|
May 19, 1992
|
Outer lead bonding head and method of bonding outer lead
Abstract
A nozzle shaft is moved down, and a semiconductor chip sucked to the lower
end of the nozzle shaft is placed on a circuit board. Then, a thermally
press-bonding member is moved down, and the outer leads of the
semiconductor chip are pressed to the circuit board by the thermally
press-bonding member. Thereafter, the thermally press-bonded member is
pressed by pressing means to strongly press the outer leads to the circuit
board, the thermally press-bonding member is then raised to release the
pressing state, and the outer leads are thermally press-bonded to the
circuit board.
Inventors:
|
Hidese; Wataru (Chikushino, JP)
|
Assignee:
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Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
|
Appl. No.:
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626060 |
Filed:
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December 13, 1990 |
Foreign Application Priority Data
| Dec 19, 1989[JP] | 1-330755 |
| Dec 19, 1989[JP] | 1-330756 |
Current U.S. Class: |
29/840; 29/740; 29/741; 29/743; 228/6.2; 228/180.22 |
Intern'l Class: |
H05K 003/30; H05K 003/34 |
Field of Search: |
29/743,740,741,840
228/5.5,6.2,180.2,222
|
References Cited
U.S. Patent Documents
3883945 | May., 1975 | Wallis | 228/180.
|
4300715 | Nov., 1981 | Keizer et al. | 228/180.
|
4787548 | Nov., 1988 | Abbagnaro et al. | 228/6.
|
4979664 | Dec., 1990 | Lyons et al. | 228/180.
|
Primary Examiner: Echols; P. W.
Attorney, Agent or Firm: Lowe, Price, LeBlanc & Becker
Claims
What is claimed is:
1. An outer lead bonding head comprising a vertically movable nozzle shaft
having a suction unit to hold a semiconductor or chip semiconductor at a
lower end thereof, a thermally press-bonding member provided independently
of the suction unit at the side of the suction unit, heating means for
heating the thermally press-bonding member, means to vertically move said
thermally press-bonding member independent of said heating means and said
suction unit for providing a space between said heating means and said
thermal press-bonding member for control of heating said thermal
press-bonding member and pressing means for pressing the thermally
press-bonding member to outer leads of the semiconductor placed on a
circuit board by said suction unit.
2. An outer lead bonding head according to claim 1, wherein said heating
means has a heat transfer member for contacting said thermally
press-bonding member to heat said thermally press-bonding member through
the heat transfer member.
3. An outer lead bonding head comprising a nozzle shaft having a suction
unit to hold a semiconductor or chip semiconductor at a lower end thereof,
heating means, and a thermally press-bonding member separate from said
heating means at the lower portion of said heating means and movable with
respect to said heating means for control of heating of said thermal
press-bonding member, said thermal press-bonding member for thermally
press-bonding to the circuit board outer leads of the semiconductor or
chip placed on a circuit board by said suction unit.
4. A method of bonding outer leads comprising the steps of moving down a
nozzle shaft, placing a semiconductor chip suctioned to the lower end of
said nozzle shaft on a circuit board, preheating a thermally press-bonding
member, then moving down the thermally press-bonding member, pressing the
outer leads of the semiconductor chip to the circuit board, using a weak
force then further pressing the thermally press-bonding member using a
stronger force to strongly press the outer leads to the circuit board,
then moving up the thermally press-bonding member to release the pressing
state, thereby providing thermally press-bonding of the outer leads to the
circuit board.
5. An outer lead bonding head comprising a vertically movable nozzle shaft
having a suction unit to hold a semiconductor or chip semiconductor at a
lower end thereof, a thermally press-bonding member disposed at the side
of said suction unit for thermally press-bonding outer leads placed on a
circuit board by said suction unit to the circuit board, and cooling means
for blowing chilled gas to the thermally press-bonding member.
6. An outer lead bonding head according to claim 5, wherein an erecting
tube for containing said nozzle shaft and a pipe for feeding chilled gas
to said erecting tube are provided, and chilled gas is blown from the
lower end of said erecting tube downward.
7. A method of bonding outer leads, comprising the steps of moving down a
nozzle shaft, placing the outer leads of a semiconductor chip suctioned to
a suction portion at the lower end of said nozzle shaft onto electrodes of
a circuit board, then moving down a thermally press-bonding member heated
by a heating means, pressing said press-bonding member onto the outer
leads, thereby to melt said electrodes, subsequently blowing a chilled gas
to said press-bonding member to cool the press-bonding member and the
electrodes, and raising the press-bonding member to release the pressure,
thereby providing thermally press-bonding of the outer leads onto the
electrodes formed on the circuit board.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an outer lead bonding head and a bonding method
thereof and, more particularly, to means for thermally press-bonding outer
leads of semiconductor chips manufactured by a TAB (Tape Automated
Bonding) method on a circuit board.
2. Description of the Prior Art
The TAB method is known to manufacture semiconductor chips by mounting the
semiconductors on a film carrier made of a synthetic resin film and
punching the film carrier.
The semiconductor chip manufactured as described above has outer leads
formed by punching the film carrier as above, and it is generally called
"an outer lead bonding" to bond the outer leads to electrodes formed on a
circuit board.
Since the outer lead is extrafine, narrow at its pitch, and formed of
extremely thin synthetic resin, the body of the lead is very weak, and it
is remarkably difficult to accurately bring and bond the outer lead to the
extrafine electrode formed on the circuit board.
A solder to be the material of the electrodes has melting and solidifying
temperature characteristics, though depending upon sorts of the solders.
It is generally desirable to gradually heat the solder up to 160.degree.
to 180.degree. C., to then rapidly heat it to 220.degree. C. or higher to
melt it, to then gradually cool it to solidify it. Since the outer lead is
extrafine and extremely thin and formed of the synthetic resin such as
polyimide, its quality is changed if it is rapidly heated to a high
temperature not to be preferable and hence it should be gradually heated.
As described above, since the bonding conditions of the outer lead are
extremely severe, outer lead bonding technique is not yet established at
present.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a bonding means which can
accurately bond extrafine and extremely thin outer leads manufactured by
the TAB method accurately to a circuit board.
In order to achieve this and other objects according to the present
invention, there is provided a bonding head of an outer lead comprising a
vertically movable nozzle shaft having a sucking unit for a semiconductor
or chip semiconductor at a lower end thereof, a thermally press-bonding
member vertically movably provided at the side of the sucking unit but
independently of the sucking unit, heating means for heating the thermally
press-bonding member, and pressing means for pressing the thermally
press-bonding member to the outer leads, thereby to thermally press the
outer leads of the semiconductor placed on a circuit board by said sucking
unit.
With the arrangement described above, the semiconductor chip sucked to the
sucking unit is placed on the circuit board, and the thermally
press-bonding member which has been heated is pressed to the outer leads
of the semiconductor chip, and if the pressing state is then released, the
outer leads are bonded to the circuit board.
These and other objects and features of the present invention will become
apparent from the following detailed description in conjunction with the
attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of an embodiment of a bonding head according
to the present invention;
FIG. 2 is a perspective view, partly in section, of the bonding head;
FIG. 3 is a sectional view of a cooling means; and
FIG. 4(a), 4(b), 4(c), 4(d), 4(e) and 4(f) are front views of operating
sequence.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will now be described with reference
to the accompanying drawings.
FIG. 1 is the perspective view of the bonding head of the present
invention, and FIG. 2 is a perspective view partly cut out of the bonding
head. An erecting tube 2 is mounted at the center of a plate-shaped
supporting frame 1. A nozzle shaft 3 is vertically movably inserted into
the tube 2, and a sucking unit 4 for sucking a semiconductor chip P is
provided at the lower end of the nozzle shaft 3. The semiconductor chip P
is manufactured by the TAB method. As shown in FIG. 3, extrafine and
extremely thin outer leads L which are formed by punching a film carrier
extend from the four sides of the semiconductor C in four directions. The
outer leads L extend from two sides of the semiconductor C in two
directions in some cases, and the means of the present invention can also
be applied to such a semiconductor chip.
A heat block 5 is provided as a heating means on the lower surface of the
supporting frame 1. The erecting tube 2 passes through the heat block 5.
In FIG. 2, electric wires 12 are provided. A heat transfer 6 which becomes
narrower toward its end integrally protrudes from the lower surface of the
heat block 5. A thermal press-bonding member 7 is provided at the side of
the sucking unit 4 in a rectangular frame shape surrounding the sucking
unit 4 to be brought into press contact with the outer leads L extending
in the four directions, and has in its sectional shape a large portion 7a
and a small-sized pressing portion 7b. As will be described in detail, the
pressing portion 7b is pressed to the outer leads L to be thermally
press-bonded to electrodes made of the solder formed on the circuit board.
The large portion 7a is a heat accumulator. The thermal press-bonding
member 7 may be formed integrally with the heat block 5. In this
embodiment, the press-bonding member 7 is separately formed from the heat
block 5 so that only the press-bonding member 7 can be replaced for
changing the sort of the semiconductor chip. In this case, when outer
leads L extend in the two directions, the press-bonding member may not be
necessarily formed in the rectangular frame shape, but formed in shape
corresponding to the outer leads L of the two directions.
In FIG. 2, a frame-shaped bracket 8 is arranged to surround the heat block
5, and the press-bonding member 7 is coupled to the bracket 8 through a
shaft 9. A coil spring 10 biases the press-bonding member 7 downward, and
a bearing 11 guides the shaft 9 up or down.
In FIGS. 2 and 4(a), a contacting-and-separating means 14 moves the
press-bonding member 7 upward or downward to contact to or separate from
the heat transfer 6, and has an arm 15 mounted rotatably around a pin 16
on the mounting plate 22 of the lower surface of the supporting frame 1.
The arm 15 is provided at its front portion with a roller 17 contacting
the lower surface of the bracket 8. A spring 18 biases the roller 17
downward, i.e., in a direction for separating the press-bonding member 7
from the heat transfer 6 downward. A rod 19 is suspended from a frame 21
(FIG. 1), and pressed at its lower end at a roller 20 supported to the
other end of the arm 15 to push the roller 17 to the lower surface of the
bracket 8 against the spring force of the spring 18. As will be described
in detail, the press-bonding member 7 is brought into contact with or
separated from the heat transfer 6 so as to make or break the heat
transferring from the heat transfer 6 to the press-bonding member 7,
thereby controlling the temperature of the press-bonding member 7. Under
the connecting condition where the press-bonding member 7 moves up, the
small interval t is secured between the heat transfer 6 and the
press-bonding member (see the enlarged part in FIG. 4(a)), whereby the
press-bonding member 7 is prevented from overheating by the heat transfer.
In FIG. 4(a), a shaft 23 stands on the upper surface of the supporting
frame 1. A multi-stage cylinder 24 is provided on the shaft 23, and a rod
25 is contacted with the upper surface of the shaft 23. The rod 27 of a
second cylinder 26 is coupled to the upper surface of the supporting frame
1. The second cylinder 26 supports the loads of the supporting frame 1 and
the heat block 5, etc. by its retracting force F2 FIG. 4(c)) The cylinder
24 is a pressing means for strongly pressing the press-bonding member 7 to
the outer leads L and serves as an elevation means for vertically moving
the press-bonding member 7 independently of the sucking unit 4.
In FIG. 4(a), a pulse motor 40 moves up or down the nozzle shaft 3 to
rotate a threaded lever 41 to move up or down a nut 42 engaged with the
threaded lever 41. A block 43 is mounted on the upper end of the nozzle
shaft 3, and the nozzle shaft 3 is biased downward by a coil spring 44. A
shaft 45 is pressed at its upper end to the nut 42, and a roller 46 is
mounted on the lower end for pressing the lower surface of the block 43.
An elevation guide block 47 of the shaft 45, and a coil spring 48 for
biasing upward the shaft 45 are provided. In the drawings, the biasing
directions of the springs are denoted by arrows.
When the pulse motor 40 is operated to move the nut 42 down, the shaft 45
moves down against the elastic force of the coil spring 48 to move the
roller 46 downward, and the nozzle shaft 3 is moved down by the elastic
force of the coil spring 44. When the nut 42 is moved up, the shaft 45 is
raised by the elastic force of the coil spring 48, and the nozzle shaft 3
is lifted by the roller 46.
In FIG. 1, a motor 50 rotates the nozzle shaft 3 around its axis. There is
provided a cam 51, a cam follower 52, a rotor 53 mounted with the cam
follower 52, and a shaft 54 suspended from the rotor 53. A roller 55 is
mounted at the end of the rod 56 extending from the nozzle shaft 3 for
pressing the shaft 54. These means horizontally rotate the semiconductor
chip P sucked to the sucking unit 4 to correct the direction and position
in the direction .theta., but do not directly relate to the present
invention, and the detailed description thereof will be omitted.
FIG. 3 shows cooling means. An inner tube 13 is inserted between the nozzle
shaft 3 and the erecting tube 2. A chilled gas is fed between the erecting
tube 2 and the inner tube 13 through a pipe 28 to be arbitrarily blown
from the lower end of the tube 2 toward the pressing portion 7b of the
press-bonding member 7 for pressing the outer leads L (arrows with dotted
lines). The pipe 28 is connected to the upper part of the erecting tube 2,
and the blown chilled gas is moved down between the tube 2 and the inner
tube 13. Accordingly, the chilled gas cools the nozzle shaft 3 over the
entire length. Thus, the nozzle shaft 3 is prevented from being
excessively heated and thermally deformed by the heat block 5 to prevent
an error from occurring in the bonding. The temperature of the chilled gas
is, for example, at the ambient temperature. A space is also provided
between the nozzle shaft 3 and the inner tube 13 thereby interrupting the
heat of the heat block 5 to be transferred to the nozzle shaft 3. When
chilled gas is blown from the lower end of the tube 2 inserted with the
nozzle shaft 3, it goes in the four directions to uniformly apply to the
pressing portion 7b disposed to surround the sucking unit 4. A chilled gas
blowing means may be separately provided from the tube 2 and the heat
block 5 to blow the chilled gas from obliquely above the press-bonding
member 7 toward the pressing portion 7b of the press-bonding member 7. The
structure of the cooling means is not limited to the particular
embodiment.
This bonding head is composed as described above, and a method of bonding
outer leads will be described with reference to FIGS. 4(a) to 4(f).
The bonding head for sucking the semiconductor chip P at the lower end of
the sucking unit 4 is moved above the board S (FIG. 4(a)) Then, the motor
40 is driven to move down the sucking unit 4, the semiconductor chip P is
placed on the board S, and the outer leads L are landed on electrodes 30
made of the solder formed on the upper surface of the board S (FIG. 4(b)).
Then, the cylinder 24 is operated to move down the supporting frame 1. The
roller 20 is then separated from the rod 19, the arm 15 is rotated by the
elastic force of the spring 18 to allow the press-bonding member 7 to move
down and to press the pressing portion 7b to the outer leads L to thereby
press the leads to the electrodes 30 (FIG. 4(c)). In this case, if the
pressing portion 7b is abruptly pressed to the outer leads L by a strong
force, the outer leads L and the electrodes 30 are readily adversely
affected. Then, the cylinder first protrudes the rod 25 of the multi-stage
cylinder 24 with a weak force to move down the press-bonding member 7,
which rotates the arm 15 with the elastic force of the spring 18 to permit
a first pressing of the pressing portion 7b to the outer leads L with a
weak force (FIG. 4(c)) Thereafter, when the heat transfer 6 lands on the
press-bonding member 7, the protruding force Fl of the rod 25 of the
multi-stage cylinder 24 is increased to press the pressing portion 7b to
the outer leads L strongly (FIG. 4(d)).
Then, the rod 25 of the cylinder 24 is retracted upward to raise the heat
block 5 (FIG. 4(e)) The press-bonding member 7 is separated from the heat
transfer 6 in this state, and the pressing state of the outer leads L is
maintained by the elastic force of the spring 18. Thereafter, the rod 27
is raised to separate the press-bonding member 7 from the outer leads L,
and the bonding work is finished (FIG. 4(f)).
The solder serving as the electrodes 30 has the following melting and
solidifying temperature characteristics. The solder is desirably melted by
heating it up to 160.degree. to 180.degree. C., then rapidly heating it to
220.degree. C. or higher to melt it, and then gradually cooling it to
solidify it. Therefore, in the apparatus, the heating temperature of the
electrodes 30 is controlled as below.
The temperature of the heat block 5 is always constant at
200.degree.-230.degree. C., but the press-bonding member 7 is preheated to
approx. 160.degree.-180.degree. C. because of the small interval t and the
heat transfer 6. Then, as shown in FIG. 4(c), the press-bonding member 7
is moved down and lands on the outer leads L to gradually heat the
electrodes 30 while pressing the outer leads L.
Subsequently, as shown in FIG. 4(d), the heat transfer 6 lands on the
press-bonding member 7 and the temperature of the press-bonding member 7
is rapidly raised to 220.degree.-230.degree. C. to completely thermally
melt the electrodes 30. Under such a condition the outer leads L are
forcibly pressed to the electrodes 30 by the protruding force F1 of the
rod 25 of the cylinder 24, thereby to thermally press-bond the outer leads
L to the electrodes 30.
Then, as shown in FIG. 4(e), the heat transfer 6 is raised and separated
from the press-bonding member 7 to interrupt the heat transfer to the
press-bonding member 7. The chilled gas is blown as indicated by the
dotted arrows to cool the press-bonding member 7 and the electrodes 30 to
180.degree. C. or lower and to maintain the pressing state by the
press-bonding member 7. If the electrode 30 is heated to 220.degree. C. or
higher and the press bonding member 7 is then rapidly moved up together
with the heat transfer 6 to cancel or release the pressure on the outer
leads L, the outer leads L will spring back from the electrode 30 which is
still molten. Therefore, as described above, the pressure on the center
leads L is still maintained after the heat transfer 6 has been moved up,
and the electrodes 30 are cooled to about 180.degree. C., and when there
is no danger of said spring-back, the press-bonding member 7 should be
moved up to cancel the pressure on the outer leads. As shown in FIG. 4(f),
when the pressed state of the press-bonding member 7 is released, the
blowing of the chilled gas is stopped, the electrodes 30 are gradually
cooled to solidification, and the outer leads L are fixed to the
electrodes 30.
As described above, the means of the invention is provided with the
press-bonding member 7 separately movable with respect to the heat block 5
of the heating means, provided with means for blowing the chilled gas
toward the pressing portion 7b and the electrodes 30. Therefore, the
electrodes 30 can be preferably heated to be melted, and the outer leads L
can be accurately bonded to the electrodes 30. Said temperatures as
180.degree. or 220.degree. C. are merely exemplified, and the temperature
depends upon the sort of the solder.
According to the present invention as described above, the outer leads can
be accurately bonded to the electrodes of the board by the thermally
press-bonding member. The press-bonding member is separably contacted to
the heating means, thereby enabling to control the heating temperature of
the electrodes for preferably thermally melting the electrodes. Since the
temperature of the press-bonding member may be also controlled by the
cooling means, the press-bonding member of relatively low temperature is
first pressed to the outer leads, and the temperature of the press-bonding
member is then raised to heat the outer leads and the electrodes to high
temperature, whereby the outer leads are scarcely changed in quality,
while satisfying the temperature characteristics of the electrodes to
preferably thermally press-bond the outer leads to the electrodes.
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